The use of printed circuit boards and ceramic substrates in making up electronic circuits is well-known. Various electrical components, such as resistors, capacitors, inductors, transformers, and transistors are mounted on the printed circuit board by soldering the leads from the components to conductors formed on the surface of the printed circuit board. More recently, leadless components have come into use which are provided without electrical leads, but which can still be soldered directly to the conductors formed on the printed circuit boards. The result has been higher reliability, lower cost, and a saving in board area, allowing more components to be attached to the circuit board or the circuit board made substantially smaller.
Monolithic ceramic capacitors, for example, are available in which the conductive plates of the capacitor are embedded in a ceramic body. The plates are arranged in alternate sets which are electrically connected to external electrode terminals in the form of metalized pads on the opposite ends of the ceramic body. The metalized surfaces can be directly soldered to the printed circuit board. Inductor components include a spool secured to the surface of an alumina chip. Metalized pads are formed on opposing edges of the chip and a wire or conductor wound on the spool is soldered to the metalized pads. Transformers have been made in the same way. The metalized pads are soldered directly to the printed circuit board.
In the past, it has been the practice to provide a single power supply for providing DC power to one or more printed circuit boards which together form an electronic circuit. As the size and cost of transistors and other circuit components have decreased, it has been found advantageous to provide each printed circuit board with its own power supply. There has therefore developed a need for a low-pass filter component which can be attached directly to the printed circuit board to provide filtering of rectified AC voltage. The present invention is directed to a leadless .pi.-filter component which can be used as power supply filter and which can be soldered directly to a printed circuit board as a single circuit component.
In brief, the present invention provides a .pi.-filter comprising a monolithic ceramic capacitor chip including two groups of parallel conductive plates embedded in a ceramic block. The plates of each group are arranged in two interleaved sets. A first set of plates for both groups extend to a common face of the chip on which is formed a single conductive electrode terminal in the form of a metalized layer on the face of the chip. Each of the other sets of plates of the respective groups are each connected to two separate conductive electrode terminals spaced along an opposing face of the chip. An inductor includes a bobbin secured to another face of the chip. Extending between the two electrode terminals on one face of the chip is a conductor wound on the bobbin to form an inductive coil, opposite ends of the conductor being electrically connected to the two electrode terminals.